Icy Moon Creates Extra Northern Lights on Saturn

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A shimmering patch of light as big as Sweden detected at the
north pole of Saturn is the spectacular result of a giant stream
of electrically charged particles from the planet's moon
Enceladus, scientists find.

On Earth, surges of charged particles from the sun colliding with
our planet's magnetic field create the northern and southern
lights, or auroras. Similar patches of light have
been seen on Jupiter, caused by electrons and ions
originating from that planet's volcanically active moon Io.

Saturn also has its own aurora light show, which is created when
solar particles from the sun interact with the planet's magnetic
field. The new study, however, is the first time astronomers have
caught a Saturn moon creating auroras on the ringed planet.

Enceladus is an extraordinarily active moon, with "ice volcanoes"
(cryovolcanoes) that spray water vapor and organic particles into
space. Researchers had long suspected that would cause
aurora-like spots on Saturn. However, space telescopes gazing at
the ringed planet failed for years to find any evidence of such
patches. [ Video:
Saturn's Spectacular Aurora ]

Now, using NASA's Cassini spacecraft in orbit around Saturn,
researchers have finally detected signs of these lights.

The
eruptions on Enceladus create a massive cloud of electrically
charged plasma that shoots electrons and ions 150,000 miles
(240,000 kilometers) along magnetic field lines to blast Saturn's
north pole. The resulting spot of light measures about 750 miles
(1,200 kilometers) by about 250 miles (400 kilometers), covering
an area slightly larger than California. Scientists compared it
to Sweden.

At its brightest, the patch shines with an ultraviolet light far
less intense than Saturn's polar aurora but comparable to the
faintest Earth aurora visible without a telescope. [ Photos:
Saturn's Rings and Moons ]

The scientists note this patch appears to vary in brightness by
up to a factor of three, suggesting Enceladus spews out matter at
a very non-constant rate.

"The electron beams flicker with timescales on the order of
minutes," said researcher Abigail Rymer, a Cassini team scientist
based at Johns Hopkins University. "It is a very dynamic
interaction."

Although it remains unclear what specifically is driving the
cryovolcano activity at Enceladus, "one thing is clear: Enceladus
cannot vent at this rate forever," Rymer told SPACE.com.
"Scientists have been wondering whether the venting rate is
variable, and these new data suggest that it is."

The scientists detailed their findings in the April 21 issue of
the journal Nature.

Follow SPACE.com contributor Charles Q. Choi on Twitter @cqchoi. Visit
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